The present application relates to a plasma display panel for use in a plasma display apparatus.
Plasma display panels (hereinafter referred to as “PDP”) display an image by generating an ultraviolet radiation from a plasma discharge of a rare gas such as Ne, Xe, Ar, or the like, and exciting a phosphor with the ultraviolet radiation to emit visible light.
The PDPs are classified into AC-driven PDPs and DC-driven PDPs. The AC-driven PDPs are better than the DC-driven PDPs as to luminance, emission efficiency, and longevity, and are main-stream PDPs.
FIG. 5 of the accompanying drawings is a fragmentary sectional perspective view of an AC-driven PDP in the past. In FIG. 5, the AC-driven PDP in the past has a front panel 1 and a rear panel 2 which are disposed in facing relation to each other.
The front panel 1 has a front glass substrate 11 which is transparent and insulative and a plurality of pairs of parallel discharge-maintaining electrodes 12a, 12b disposed on the lower surface of the front glass substrate 11 and spaced at a given pitch. The discharge-maintaining electrodes 12a, 12b include transparent electrodes. The front panel 1 also includes a dielectric layer 14 disposed on the lower surface of the front glass substrate 11 in covering relation to the pairs of discharge-maintaining electrodes 12a, 12b, and a protective layer 15 disposed on the lower surface of the dielectric layer 14. Bus electrodes 13a, 13b are disposed on the respective lower surfaces of the discharge-maintaining electrodes 12a, 12b for reducing the wiring resistance thereof.
The bus electrodes 13a, 13b on the lower surfaces of the discharge-maintaining electrodes 12a, 12b extend parallel to the discharge-maintaining electrodes 12a, 12b and are narrower than the discharge-maintaining electrodes 12a, 12b. 
The dielectric layer 14 on the lower side of the discharge-maintaining electrodes 12a, 12b has an inherent current limiting function which gives the AC-driven PDP a longer service life than the DC-driven PDPs. The dielectric layer 14 is generally formed by printing and baking a layer of glass having a low melting point.
The protective layer 15 serves to prevent the dielectric layer 14 from being sputtered by the plasma discharge. The protective layer 15 needs to be made of a material which is highly resistant to sputtering. Specifically, the protective layer 15 is often made of magnesium oxide (MgO). Since MgO has a large secondary electron emission coefficient, the protective layer 15 is also effective to lower the discharge starting voltage.
The rear panel 2 has a rear glass substrate 21 which is transparent and insulative and a plurality of address electrodes 22 for writing image data, disposed on the upper surface of the rear glass substrate 21 and extending perpendicularly to the pairs of discharge-maintaining electrodes 12a, 12b of the front panel 1. The rear panel 2 also includes a dielectric layer 23 disposed on the upper surface of the rear glass substrate 21 in covering relation to the address electrodes 22, a plurality of partitions 24 extending parallel to the address electrodes 22 and disposed on the dielectric layer 23 at respective positions substantially intermediate between adjacent ones of the address electrodes 22, and a plurality of phosphor layers 25 disposed in regions between adjacent ones of the partitions 24 and extending up to upper ends of the partitions 24.
The phosphor layers 25 include a plurality of sets of adjacent phosphor layers 25R, 25G, 25B coated with materials for emitting red (R) light, green (G) light, and blue (B) light, respectively. Each set of phosphor layers 25R, 25G, 25B provides pixels.
Between the front and rear panels 1, 2 which confront each other, there are provided striped discharge spaces 4 each surrounded by two adjacent partitions 24, the protective layer 15 on the lower surface of the front glass substrate 11, and the phosphor layer 25 between the partitions 24 above the rear glass substrate 21.
The discharge spaces 4 are filled with a rare gas such as Ne, Xe, Ar, or the like under the pressure of about 66.5 kPa. When an AC voltage having a frequency ranging from several tens to several hundreds kHz is applied through the bus electrodes 13a, 13b between the discharge-maintaining electrodes 12a, 12b, a plasma discharge occurs in the rare gas, exciting rare gas molecules. When the excited rare gas molecules return to the ground state, they generate an ultraviolet radiation which excites the phosphor layers 25 to emit light.
The phosphor layers 25R, 25G, 25B emit R, G, B lights, respectively. The address electrodes 22 are selectively energized to select desired pixels to emit light in desired colors for thereby displaying a color image on the plasma display panel.
When the AC voltage applied through the bus electrodes 13a, 13b between the discharge-maintaining electrodes 12a, 12b, as shown in FIG. 6 of the accompanying drawings, a displacement current flows to charge an electrostatic capacitance 40 having a dielectric body provided by the front glass substrate 11 between the discharge-maintaining electrodes 12a, 12b and an electrostatic capacitance 41 having a dielectric body provided by the dielectric layer 14 between the discharge-maintaining electrodes 12a, 12b. 
The displacement current is a reactive current which does not directly contribute to the display of the image, and causes resistive components of the discharge-maintaining electrodes 12a, 12b and a control circuit therefor to produce a loss, tending to produce a reactive power.
As the reactive power increases, not only the power consumption of the AC-driven PDP for displaying images, but also the power consumption of IC circuits for energizing the AC-driven PDP increase. As a result, the IC circuits generate heat and become unstable in operation.
In order for the AC-driven PDP to have a higher resolution, it is necessary to employ a greater number of pairs of discharge-maintaining electrodes 12a, 12b. As the number of pairs of discharge-maintaining electrodes 12a, 12b increases, the electrostatic capacitance per panel increases, and since the front glass substrate 11 is of a relatively large relative permittivity of about 8, the electrostatic capacitance 40 becomes relatively large, resulting in an increase in the reactive power. Inasmuch as it is important for the AC-driven PDPs to have lower power requirements, there have been demands for reduced electrostatic capacitances 40, 41 for reduced reactive power.
Japanese patent laid-open No. 2003-197110 discloses a PDP including a dielectric layer made of a glass material containing B2O3 and SiO2 as chief components, the dielectric layer being disposed between a front glass substrate and a plurality of pairs of discharge-maintaining electrodes for thereby reducing the electrostatic capacitances.
However, the disclosed PDP structure fails to sufficiently reduce the electrostatic capacitances.